Techno-economic and environmental analysis of organic municipal solid waste for energy production

Addressing the critical conundrum of escalating municipal solid waste (MSW) and shrinking landfill spaces in urban areas, this research pioneers a sustainable approach for Bangladesh by exploring the potential of biogas production from MSW. Distinctly, it fills the research gap by providing a detailed techno-economic and environmental analysis of decentralized fixed-dome anaerobic digestion facilities in the urban context of Chittagong, Bangladesh, a domain previously underexplored. Our findings demonstrate the feasibility of converting MSW into a renewable energy source, offering an innovative solution that simultaneously tackles waste management and energy generation challenges. Each proposed plant showcases the capability to generate 536 m³ of biogas daily, sufficient to power a 50 kW gas engine and supply 44 households, thereby contributing significantly to urban waste reduction and CO2 emissions mitigation by approximately 500 tons monthly. The economic analysis reveals an attractive investment payback period of two years, underscoring the model's viability and its potential as a replicable framework for similar urban settings grappling with waste management crises. This study not only bridges a critical knowledge gap but also introduces a novel, sustainable waste-to-energy model, marking a pivotal step towards achieving energy security and environmental sustainability in developing nations.


Introduction
The growing amount of municipal solid waste (MSW) and its detrimental environmental effect compelled the world to focus on the careful management of MSW.According to the World Bank, humans produce an astonishing 2 billion tons of MSW annually [1].By • The ingredients and the quality of the MSW were examined.
• A digester of the specific size, which can be made locally, has been designed.
• Calculated the amount of biogas generation and equivalent electrical energy generation.
• Accomplished the financial analysis to set up a plant while considering the payback periods.
• Studied the environmental effect by reducing MSW by 90 % and mitigating GHG by 93 % compared to the base case (coal fired power plant).
The unique contribution of this research lies in its application of waste management technologies in the context of a developing nation, offering detailed techno-economic analysis and highlighting the importance of local customization and design innovation.By providing valuable insights into the feasibility, cost-effectiveness, and environmental impacts of AD technology, the study arms policymakers and stakeholders with critical information necessary for assessing its viability for sustainable waste management and energy production.Illustrating economic incentives, including substantial cost savings and the generation of revenue from energy sales, the research underscores AD's pivotal role in driving sustainable economic progress, promoting energy independence, and facilitating job creation, all while alleviating environmental degradation.This research presents a sustainable waste management approach that significantly reduces environmental pollution by converting organic waste into biogas instead of landfills.This method mitigates methane emissions, a potent greenhouse gas, contributing to cleaner air and a healthier environment for communities.The conversion of organic waste into biogas and electricity provides an alternative and renewable energy source, addressing community energy demands.This reduces reliance on non-renewable energy sources and improves energy accessibility, particularly in areas with scarcity.Implementing AD also promotes efficient and sustainable waste management reducing the waste needed for landfilling and encouraging responsible waste disposal and recycling within communities.Proper waste management directly impacts public health by minimizing the risks associated with uncontrolled waste disposal.AD reduces hazardous practices, leading to cleaner surroundings and improved public health conditions.This research also aligns with the principles of a circular economy by converting waste into valuable resources like biogas and electricity, promoting the reuse of organic matter, and reducing the linear 'take-make-dispose' S. Alam et al. model.This approach contributes to a more sustainable and resource-efficient system, fostering a circular economy mindset.The article also discusses the growing challenge of MSW management and proposes a sustainable solution through WtE technologies.It emphasizes the environmental impacts and potential energy generation from source-separated organic waste, aligning with global sustainability goals.The research advances AD technology for MSW treatment, highlighting its energy generation potential and economic feasibility compared to traditional disposal methods.The research offers practical design parameters for AD systems, financial evaluations, and site selection considerations, aiding policymakers and stakeholders in making informed decisions for implementing waste management solutions.The article holds global relevance as it addresses a universal issue of MSW management.It offers a blueprint for integrating technology, economics, and environmental concerns in seeking effective waste-to-energy solutions.Focusing on WtE via AD, this methodology tackles the global challenge of MSW management and significantly contributes to various Sustainable Development Goals (SDGs) [22].The main focus is achieving Goal 7 by prioritizing WtE through anaerobic digestion.This approach promotes using renewable and readily available energy sources while reducing dependence on fossil fuels.Furthermore, it contributes to the achievement of Goal 11 by effectively overseeing the disposal of municipal solid waste, reducing landfill trash, and promoting cleaner urban surroundings.The transition from a linear to circular economic model, following Goal 12, focuses on responsible consumption through the conversion of trash into energy, emphasizing sustainable waste management practices.The initiative effectively addresses Goal 13 by actively reducing methane emissions and greenhouse gases during waste decomposition, significantly contributing to greater climate mitigation efforts.Moreover, it is in line with Goal 9 as it demonstrates ingenuity in waste management methods, namely in the design and effectiveness of digesters.The research highlights the importance of meticulous financial planning and investment in waste-to-energy plants, recognizing its initial expenses.This article is structured to guide the reader through a comprehensive analysis of the feasibility, economic viability, and environmental benefits of utilizing anaerobic digestion for biogas production from municipal solid waste in Bangladesh.Following the introduction in Section 1, Section 2 outlines the Research Methodology, detailing the study area, data collection processes, and the analytical methods employed.Section 3, Results, presents the key findings related to biogas yield, energy production capacity, and potential environmental impacts.Section 4, Discussion, interprets these results in the context of Bangladesh's waste management and energy challenges, comparing them with global practices and highlighting the study's innovation and significance.The Financial Analysis in Section 5 examines the economic feasibility and investment returns of the proposed anaerobic digestion facilities.Section 6 delves into the Environmental Impact Assessment, evaluating the project's potential to reduce greenhouse gas emissions and contribute to sustainable waste management.Finally, Section 7, Conclusions and Future Directions synthesizes the study's findings, discussing their implications for policy, practice, and further research.

Research methodology
The article explores the design, sizing, and feasibility of an anaerobic digester system for converting organic municipal solid waste into energy.It uses RETScreen software for techno-economic analysis and conducts an environmental impact assessment.The process optimization is discussed, focusing on feedstock composition, dilution ratios, and biogas production potential.The system's capability to produce biogas for electricity generation and household use is evaluated.The article also discusses the technical feasibility and Fig. 1.Flowchart of research methodology.
S. Alam et al. challenges of implementing anaerobic digestion technology in developing countries, focusing on local expertise, materials availability, construction, and maintenance.The flow chart of the research methodology of this paper is shown in Fig. 1.
The article offers valuable insights into process engineering design and implementation in waste-to-energy projects.The article discusses the growing challenge of MSW management and proposes a sustainable solution through WtE technologies.

Data collection and analysis
The quantity and quality of waste in Chittagong, Bangladesh, have been analyzed using primary data from the Chittagong City Corporation authority.The annual waste generation rate ranged from 2000 tons per day (TPD) to 2400 TPD from 2016 to 2019, with an upward trend.The waste generation rate increased by over 500 TPD over the last decade (Fig. 2).However, the coronavirus effect significantly dropped waste generation in 2020, especially during the lockdown period.After the lockdown, waste generation rose again, with a peak in August.The city's waste generation also varies with season and festival, with higher vegetable production in winter increasing waste production by around 5 %.Waste generation also rises during festivals like 'Pahela Baishakh' in April and 'Eid ul Adha'.The waste composition was determined using the quartering process, which was done within four to 5 h to minimize degradation.The waste was then divided into four sections: A, B, C, and D, with the remaining two sections omitted.Repeating these steps yielded almost 15 kg of waste.
The whole waste collection and sorting process has been shown in Fig. 3(a-c).The quantity and quality of waste in Chittagong, Bangladesh, have been analyzed using primary data from the Chittagong City Corporation authority shown in Fig. 3a.Following reduction, the decreased sample was physically divided into various categories, including food waste, fabric, paper, plastic and others.As seen in Table 1, it was discovered that food makes up a sizable amount of the waste (around 80 %).Proximate analysis of the collected sample showed that it included 79.3 % moisture, 17.3 % volatiles, 2.2 % ash, and 0.9 % fixed carbon.
The study conducted a proximate analysis at the Asian Institute of Technology (AIT) laboratory to understand the composition and characteristics of municipal solid waste used in AD.The analysis involved drying a sample in an oven at 105 • C until a constant weight was achieved, determining the moisture content.Volatile matter was measured by heating the sample in a muffle furnace at 950 • C without air, recording the loss in weight.Ash content was determined by burning the remaining material post-volatile matter analysis in a muffle furnace at 575 • C until a constant weight was achieved.The fixed carbon content was calculated by subtracting the sum of the percentages of moisture, volatile matter, and ash from 100 %.The results of the proximate analysis provided essential data on the waste composition, particularly moisture and organic content, which are critical factors in the efficiency of the AD process.The analysis revealed that the MSW sample contained a significant amount of organic material suitable for biogas production, with a balanced moisture content conducive to the anaerobic process.The data obtained from this proximate analysis were crucial in designing the AD process, optimizing system parameters for the specific waste composition, and estimating potential biogas yield and overall efficiency.

Site selection
This study has proposed the location Halishahar for setting up a medium large-scale, decentralized biogas plant.The current dumpsite is located here, and the transports for collecting MSW are kept here.So, additional transport time and distance for MSW transport to the WtE plant will be minimal.The total area of the location is 9.64 km 2 .Around 155 k people live in this area.Considering the 0.41 kg/day per capita waste generation rate and 42 % waste collection efficiency, as shown [23], around 27 TPD MSW (around 20 TPD organic fraction of MSW) can be obtained from this area.
There is a compost plant in Halishahar that processes 5 TPD organic fraction of MSW (OFMSW) to produce organic fertilizer.Therefore, around 15 TPD OFMSW are available for processing in the WtE plant.This study has proposed three decentralized biogas plants, each having a handling capacity of 5 TPD OFMSW.Three potential sites for setting up the plants are shown in Fig. 4.

Determination of design parameters for anaerobic digester
According to Nirapod Engineering Limited, continuous, mesophilic wet digestion systems are used for biogas production in Bangladesh due to low solid content, tropical climate conditions and economic prospects.Until 1992, Indian floating dome type biogas Fig. 2. Variation of MSW generation with season.
S. Alam et al. plants were used, but all those plants have gone out of order within 3-4 years due to corrosion.In 1992, the Chinese fixed dome type model was introduced, and after that, the use of the Indian floating dome type completely stopped.Most of the digesters in Bangladesh are now fixed dome type digesters, although the largest agro-industrial biogas plant is CSTR type.Up to 600 m 3 of biogas digester (fixed dome type) can be built using local technology, experts, and materials.Above 600 m 3 , foreign experts are needed to design and construct biogas plants.For this, investment cost/m 3 increases to a great extent.Considering investment cost, availability of local experts, ease of construction and maintenance, level of use of local materials and resources, level of similar usage and performance records in Bangladesh and adaptability to future situations, this study has considered medium large-scale fixed dome digester for further analysis.
Table 2 illustrates the design parameters which were considered based on the suggestions of local experts.assumptions made for volume calculation of the fixed dome digester is shown in Table 3 [26].Whereas Table 4 shows the assumptions made for calculating the geometrical dimensions of the digester.

Table 1
Municipal solid waste composition of Chittagong city, Bangladesh.

Techno-economic analysis
Many researchers have used Aspen Plus® method to evaluate the feasibility of waste-to-energy projects [27][28][29].Aspen Plus® is one of the most powerful frameworks for optimization, architecture, sensitivity, and economic assessments compared to other process simulators.However, Aspen Plus® has a very high license cost ($2000/year for university purposes) and needs a certain degree of interface experience [30][31][32].In contrast with Aspen Plus®, RETScreen Software, in many cases, is preferred by many researchers [33,34].The key benefit of this software is that the user can customize the calculation sheets, making user-tool interaction easier.Furthermore, this free decision-making tool is designed to assess the feasibility and performance of renewable energy and energy efficiency programs.Considering the benefits, this research used RETScreen software to conduct the techno-financial analysis of the proposed power plant.RETScreen is a decision-making and capacity-building tool that several researchers have successfully used to assess various renewable energy projects.The program can conduct a five-step standard analysis, which includes an energy model, cost analysis, GHG analysis, financial analysis, and sensitivity and risk analysis.Based on the local site condition and device characteristics, the energy model estimates annual energy output by the proposed design.Pre-tax and after-tax cash flows, interest payments, income tax, asset depreciation, and financial viability metrics are all concepts used in financial analysis.The effect graph, Monte Carlo simulation, median and confidence interval, and risk analysis model validation are all part of the sensitivity and risk analysis.It is possible to assess the feasibility of a proposed design by conducting both of these analysis.

Quality control and quality assurance
Rigorous quality control (QC) and quality assurance (QA) measures were integral to the research methodology, ensuring the reliability and validity of the collected data.This encompassed a comprehensive evaluation of waste sampling and analysis techniques to reflect MSW's composition and volume accurately.Additionally, the site selection for the AD facility was critically assessed, along with the design and financial aspects of the project, ensuring adherence to established standards and practices.Applying QC and QA protocols underpinned the credibility of the study's recommendations for implementing AD technology in Chittagong, aligning with sustainable waste management and energy production goals.This detailed analysis underscores the feasibility and strategic importance of deploying AD technology in Chittagong, backed by a systematic approach to data collection, site selection, and adherence to quality standards.The proposed biogas plants in Halishahar exemplify a sustainable solution to MSW management challenges, contributing to environmental sustainability and achieving global sustainability targets in Bangladesh.

Environmental analysis
This study used the IPCC Guidelines for GHG inventory levels to estimate emissions GHG calculation tool was used to perform the calculation [28].The GHG emissions calculation tool is a free Excel-based tool developed by the Greenhouse Gas Protocol and the World Resources Institute to help people measure their GHG emissions using the GHG Protocol.
The assumption for volume calculation Description Vc = 5 % V V c = Volume of gas collecting chamber Vs = 15 % V V S = Volume of sludge layer Vgs + V f = 80 % V V gs = Volume of gas storage chamber V f = Volume of fermentation chamber Vgs = V H V H = Volume of hydraulic chamber Vgs = 0.5 (Vgs + V f + Vs) K K = Gas production rate per m 3 digester volume per day.For Bangladesh, K = 0.4
The assumption for geometrical calculation Description

Design of proposed anaerobic digestion system
Table 5 summarizes the anaerobic digestion system design parameters considered in this study.The study suggested that 5 TPD segregated OFMSW would be diluted with 7.5 m 3 water to get an 8 % concentration of TS, which is considered a favorable condition for digestion.Fig. 5a shows the cross section and Fig. 5b presents the geometric dimensions of the proposed digester.For a tropical environment with an average air temperature of 35 • C, an HRT of 30-40 days is suggested.A retention period of 35 days is used in this analysis, suggesting that this plant would need a 437.5 m 3 active reactor volume.The study has assumed that 20 % of 5 Ton is dry matter.The Volatile Solids (VS) content of the dry matter is 80 %, meaning that VS amounts to 800 kg of the 12.5 m 3 of diluted feedstock, and the share of VS amounts to 64 kgVS/m 3 .
As a result, the organic loading rate of the system would be 1.82 kgVS/m 3, which is acceptable for a non-stirred AD system (the organic loading rate should be below 2 kg VS/m 3 for a non-stirred AD system) [28].The design and obtained parameters of the fixed dome digester are shown in Fig. 4 based on the calculations in the Appendix.Assuming that OFMSW normally produces 0.67 m 3 of biogas per kgVS (considering 60 % methane content and 0.4 m 3 CH 4 /kgVS), approximately 536 m 3 of biogas should be produced per day (1.82 kgVS/m 3 day × 0.67 m 3 /kgVS × 437.5 m 3 ).Since 60 % of the biogas is methane (CH 4 ), the methane yield is 321.6 m 3 /day.According to Rahman Renewable Energy Co. Ltd., Bangladesh, to produce 1 kWh of electricity, a typical 100 % biogas generator requires 0.707 m 3 biogas.So, to run a 50 kW gas generator for 12 h, 424 m 3 biogas would be needed.The rest of the biogas (112 m 3 biogas) can provide biogas to 44 households for cooking purposes.

Financial evaluation of the proposed design
A summary of the financial evaluation of the proposed design is shown in Table 6.The financial analysis of an anaerobic digestion plant project reveals its profitability and quick returns on investment.The project's initial costs are $98,640, with no fuel costs associated with the operation.The savings are $19,899.The debt payments are $16,840, reflecting a net saving in the first year.The project generates electricity export revenue of $30,240, and no revenue from GHG reductions.The total annual savings and revenue are $30,240, and the net annual cash flow is $33,299.
The project's financial viability is measured by a 38.4 % pre-tax IRR -Assets, indicating its high profitability.The simple payback period of two years and the equity payback period of 0.86 years are noteworthy, as only a part of the investment is from equity due to the 70 % debt ratio.However, this simplified analysis does not consider potential market conditions, operational risks, or other financial factors such as taxes or changes in government incentives.
In conclusion, the project is highly profitable with quick returns on investment due to the lack of fuel costs and the ability to generate significant revenues from electricity export.

Environmental impact of proposed design
This study performed a life cycle assessment of the 5 TPD biogas plant using the GHG emission calculation tool.A summary of the analysis is shown in Table 7.The table presents a summary of greenhouse gas (GHG) emissions associated with the operational activities of an anaerobic digestion (AD) plant, as well as the emissions avoided by this process compared to conventional waste management and energy production methods.The table includes emissions from operational activities (8.62 kg CO 2 -eq/ton of organic waste), unavoidable leakages (21.0 kg CO 2 -eq/ton of organic waste), direct GHG emissions from AD (29.62 kg CO 2 -eq/ton of organic waste), avoided GHG emissions from electricity production (406.07kg CO 2 -eq/ton of organic waste), and avoided GHG emissions from  organic waste landfilling (630.00 kg CO 2 -eq/ton of organic waste).The net GHG emissions from AD (− 1006.45 kg CO 2 -eq/ton of organic waste) represent the net impact of the AD process, taking into account both direct emissions and emissions avoided by generating energy and preventing landfill gas emissions.The total GHG reduction from AD per month (− 140.96 tons CO 2 -eq/month) equates to the entire volume of waste treated by the facility in one month.Recycling can also prevent GHG emissions compared to producing goods from virgin materials, reducing emissions per ton of recyclables processed.The total monthly GHG emissions saved through recycling activities at the facility is − 78.21 tons CO 2 -eq/month.

Overview of proposed WtE recovery option for chittagong
Fig. 6 shows the proposed WtE recovery option for Chittagong.Around 27 TPD MSW is being generated in the proposed location, Halishahar.Among these, around 20 TPD are organic and 3.3 TPD are recyclable.At present, there is a compost plant that collects 5 TPD source organic waste and feeds it to the plant.Therefore, around 15 TPD organic waste is still present in the main waste stream.This study proposed building three decentralized biogas plants in Ward 37,38,and 39.
The dumpsite is situated in Ward 37 and all the dump trucks are kept there.Therefore, transportation distance and time will be comparatively lower if the plants are constructed on these sites.For Ward 37, 10 TPD sources separated organic waste to be collected to feed the compost and biogas plants.In other Wards, 5 TPD source separated waste are to be collected.Chittagong City Corporation can involve NGOs for source separate waste collection and preprocessing.Around 3.3 TPD of the waste steam is recyclable.The informal sector generally handles this recycling in Chittagong.Around 4 TPD waste is inorganic and non-recyclable, which can be dumped in the current dumpsite.Around 24 TPD waste (the informal sector separates recyclable products) is dumped from the Halishahar area without a waste treatment facility.AD can reduce waste volume by 90 % and CO 2 -equivalent emissions by 500 tons per month.This is

Activity GHG Emissions Unit
GHG emissions from operational activities 8.62 kg of CO 2 -eq/ton of organic waste GHG emissions through unavoidable leakages 21.0 kg of CO 2 -eq/ton of organic waste Direct GHG emissions from anaerobic digestion 29.62 kg of CO 2 -eq/ton of organic waste Avoided GHG emissions from electricity production 406.07 kg of CO 2 -eq/ton of organic waste Avoided GHG emissions from organic waste landfilling 630.00 kg of CO 2 -eq/ton of organic waste Net GHG emissions from anaerobic digestion (life cycle perspective) − 1006.45 kg of CO 2 -eq/ton of organic waste Total GHG reduction from anaerobic digestion per month − 140.96 ton of CO 2 -eq/month kg of CO 2 -eq/ton of mixed recyclables ton of CO 2 -eq/month Net GHG emission from recycling (life cycle perspective) − 790.01Total GHG reduction from recycling per month − 78.21 S. Alam et al. due to the breakdown of organic waste, producing biogas and digestate, which have lower volumes than the original waste.The 90 % figure is based on empirical data from specific facilities and varies based on waste composition, digester efficiency, and retention time.Anaerobic digestion captures methane, a potent greenhouse gas, preventing its release and allowing it to be used as renewable energy.
The 500 tons of CO 2 -eq/month saved is calculated based on the amount of methane emitted by landfilling the waste minus CO 2 emissions from combusting the methane collected via digestion.

Comparative analysis
The comparative analysis and critical review across four studies are shown in Table 8.

Critical analysis
The comparative analysis across the four studies reveals varied approaches to WtE technologies.Our study is unique in its local context application, specifically tailored for Chittagong, Bangladesh, focusing on source separated organic MSW.Study 1 and Study 3 also focus on financial aspects but with different technological approaches, namely AD, gasification, and co-AD plants.Study 2 diverges by concentrating on biogas upgrading and power requirements, highlighting the diversity in addressing WtE challenges.Each study has its unique focus and context, with our study standing out for its detailed techno-financial and environmental analysis, specifically for a developing country.The financial aspects are a common theme, with Study 1 providing a detailed financial model assessment, including NPV and IRR, similar to our approach.Study 2 and Study 3 contribute to the broader picture by evaluating biogas upgrading and the feasibility of Co-AD plants, respectively.The critical review indicates that while each study offers valuable insights, our work is particularly significant for its practical application in a developing country context, making it a notable contribution to sustainable waste management.

Practical application
The study presents a comprehensive framework for implementing AD technology in managing MSW, focusing on the organic fraction.It emphasizes the importance of source-separated organic waste for optimal AD functioning, providing a roadmap for waste management authorities.The study proposes medium-large fixed dome digesters designed to suit local expertise and materials, facilitating the establishment of decentralized biogas plants that ensure efficient waste-to-energy conversion.The research also highlights the financial feasibility of AD-based energy production, indicating potential revenue generation through biogas utilization.The economic analysis underscores the attractiveness of these plants for investors, with a relatively short payback period.The study also highlights the potential environmental impact mitigation, with a 93 % reduction in GHG emissions compared to coal-fired power plants.The proposed plants could positively impact local communities by providing biogas for household cooking and reducing waste volumes.This model can be replicated for developing nations facing MSW management challenges, offering a comprehensive approach  from waste composition analysis to financial feasibility.Policy recommendations are supported, emphasizing the importance of waste segregation practices.Encouraging authorities to prioritize source-separated organic waste for AD plants could drive better waste management policies.The research's outcomes serve as educational material, aiding in awareness campaigns about sustainable waste management practices.In conclusion, the practical applications of this research extend beyond the technical realm, impacting waste management policies, economic sectors, community engagement, and environmental stewardship.Implementing these insights could pave the way for a more sustainable and eco-friendly future.

Conclusion and Future Directions
This study has undertaken a comprehensive techno-economic and environmental analysis of implementing medium to large-scale decentralized anaerobic digestion (AD) plants for municipal solid waste (MSW) in Chittagong, Bangladesh.Our findings illuminate the path for sustainable waste management and energy production, offering a nuanced understanding of the potential and challenges associated with waste-to-energy (WtE) conversions in developing urban contexts.Our research makes a significant contribution to the scientific community by providing empirical evidence on the viability of AD technology in efficiently managing organic MSW and producing renewable energy in a setting like Chittagong.We have designed a feasible model for AD plants that leverages local waste characteristics and climatic conditions, enhancing the practicality and sustainability of WtE solutions.The study's scientific value lies in its detailed analysis of operational parameters, environmental impacts, and economic viability, presenting a holistic view of AD's potential to address waste management and energy challenges simultaneously.By demonstrating the technical feasibility, environmental benefits, and economic attractiveness of AD plants, our study provides a blueprint for policymakers, urban planners, and renewable energy stakeholders interested in adopting sustainable waste management practices.The model proposed can serve as a replicable framework for similar urban areas in developing countries, where waste management remains a critical issue, and the quest for renewable energy sources is ongoing.The success of the proposed AD plants heavily relies on effective source separation of organic waste, which may require significant behavioral changes and community engagement efforts.Additionally, our analysis is constrained by the assumptions made regarding technological performance and market conditions, which may evolve over time.
Building on the foundation laid by this study, future research should explore innovative approaches to enhance the efficiency and scalability of AD technology.Investigating alternative pre-treatment methods, optimizing digester design for varied waste compositions, and assessing the long-term operational challenges would be valuable.Moreover, further studies could examine the socioeconomic impacts of AD plant implementation, including job creation, public health benefits, and community acceptance.Collaborative research involving multi-disciplinary teams could also explore the integration of AD systems within broader waste management and renewable energy frameworks, maximizing the environmental and societal benefits.This study underscores the scientific and practical merits of deploying AD technology for MSW management in Chittagong, offering insights that contribute to the global discourse on sustainable urban development and renewable energy.By highlighting the opportunities, addressing the challenges, and outlining the path for future inquiry, this research advances our collective understanding of waste-to-energy solutions as a pivotal component of sustainable urban ecosystems.

Institutional review board statement
Not applicable.

Informed consent statement
Not applicable.

Fig. 4 .
Fig. 4. Proposed location for the present study.

1 = 2 = 1 = 2 =
Volume of the fermentation chamber R 1 = 0.725 D R Curvature radius of the dome R 2 = 1.0625D R Curvature radius of the bottom f 1 = D/5 f Vector rise of the dome f 2 = D/8 f Vector rise of the bottom

Fig. 5 .
Fig. 5. (a) Cross section of the proposed digester; (b) Geometric dimensions of the proposed digester.

S
.Alam et al.

Table 2
Design parameters.
S.Alam et al.

Table 5
Anaerobic digestion system design parameters.
S.Alam et al.

Table 8
Comparative analysis and critical review across four studies.